Coaxial cable and method of making same



May 10, 1955 T. J. RHODES 2,708,176

coAxIAL CABLE AND METHOD oF MAKING SAME Filed June 14, 1951A 2 sheets-sheet 1 Z7 Ji Z7 Zig@ j? il?? 5 BY fw@ .AENT

T. J. RHODES COAXIAL CABLE AND METHOD OF MAKING SAME Filed June 14. 1951 May l0, 1955 2 Sheets-Sheet 2 Coaxrai. CABLE AND METHOD oF MAKiNG SAME Thomas Si. Rhodes, Clifton, N. J., assigner to United States Rubber Company, New York, N. Y., a corporation of New .iersey Application .lune 14, 1951, Serial No. 231,450 1 Claim. (Cl. 154-228) This invention relates to an improved coaxial electric cable, and more particularly it relates to a coaxial cable provided with sealed cells along its length, as well as to a method of making such cable.

One object of the invention is to provide a coaxial cable having means for maintaining a iluid dielectric medium between an inner conductor of the cable and an outer conductor spaced from the inner conductor.

Another object is the provision of a coaxial cable that has a maximum of gaseous dielectric medium around the inner conductor.

Still another object is to provide a coaxial cable in which the central conductor is supported by a minimum amount of solid dielectric material.

Another object is the provision of a coaxial cable than can be constructed readily in either large or small 2 sizes, and that can be made highly ilexible.

Still a further object is to provide a coaxial cable having a gaseous dielectric material retained within the cable in such manner that the gas remains in the cable substantially permanently.

lt is still a further object of the invention to provide a cable embodying a gaseous dielectric, which can be cut into desired lengths without loss of the gas.

The manner in which the invention accomplishes the foregoing objects, as well as additional objects and advantages, will be made manifest in the following detailed description of the invention, which is intended to be read with reference to the accompanying drawings, wherein:

Fig. 1 is a perspective view of a length of the inner portion of a cable constructed according to the invention;

Fig. 2 is a longitudinal sectional elevation of a length of the cable taken along the line 2 2 of Fig. 1 and showing an outer conductor and insulation applied thereto;

Fig. 3 is a schematic view of an apparatus for constructing the cable according to the method of the invention;

Fig. 4 is a fragmentary longitudinal sectional view on a larger scale of a portion of the cable in process of manufacture;

Fig. 5 is a fragmentary detailed view of a portion of the apparatus for making the cable;

Fig. 6 is a more enlarged fragmentary view of a portion of the apparatus of Fig. 5; and

Fig. 7 is a sectional elevational view of an apparatus for constructing the cable by a modied method.

Referring to the drawings, and in particular to Figs. 1 and 2, the improved cable shown therein includes a central conductor 10 having a surrounding sleeve 11 of insulating material supported in spaced relation thereto. The insulating sleeve 11 is suitably made from an organic plastic material, preferably a thermoplastic material, such as polyethylene. The inner conductor l0 is supported coaxially of the sleeve 11 by periodically spaced inwardly crimped portions 12 of the sleeve 11. The crimping of each portion of the sleeve 11 is acrates Patent O 2,708,176 Patented May 10, 1955 'ice complished in a manner that will be described in detail below, and such crimping is preferably eiected at three equally spaced points around the circumference of the sleeve so as to bring the oppositely disposed walls, such as walls 13 and 14 of adjacent crimped portions, into intimate engagement along a radial line 15 of contact. In this way, the adjacent crimped portions form a solid wall 17 at spaced periodic intervals along the length of the cable. crimped area bears rmly against the surface of the central conductor 10 in sealing engagement therewith. In this way, the crimped portions of the sleeve define successive gas-tight cells 20 along the entire length of the cable. rlhe cells 20 are iilled, at the time of manufacture of the cable, with a suitable uid dielectric medium, usually a gas, such as moisture-free air, nitrogen, or other gas.

The outer surface of the insulating sleeve 11 is covered by an outer conductor 21, usually in the form of a braided wire sleeve, and an outer insulating layer 22 is superimposed over the outer conductor to complete the cable.

ln the method of making the cable illustrated in Figs. 3 to 6, a continuous length of the outer sleeve 11, suitably formed by a continuous extrusion operation in the conventional manner, and containing the conductor 1t) in its hollow interior, is fed from a suitable supply reel 25 to a guide roll 26. The cable passes from the guide roll 26 through a suitable radiant heater 27 that is designed to raise the temperature of the sleeve 11 sufiiciently to make the sleeve soft and plastic so that it can be readily deformed. The thus heated sleeve then passes through an arrangement of three crimping wheels 28, 29 and 30, arranged in 'three equally spaced planes extending radially from the longitudinal axis of the sleeve, as indicated most clearly in Figs. 5 and 6. Two

lof the crimping wheels 28, 29 are rotatably supported in standards 31 and 32 with the axis of rotation of the wheels inclined to the vertical, while the lower crimping wheel is rotatably supported on a horizontal shaft 33 extending from one standard 31 to the other standard 32. The horizontal shaft is rotated by a suitable driving mechanism 34, and bevel gears 35, 36 on the shaft 33 serve to drive similar bevel gears 37, 38 on the shafts of each of the other crimping wheels 2S, 29. The arrangement is such that the driving mechanism 34 rotates all three crimping wheels simultaneously at the same speed. Each of the crimping wheels carries at its outer periphery a series of circumferentially spaced radially extending blades 39 gage the surface of the sleeve 11 as the wheels rotate. The blades 39 are cut away at their working surfaces to present a contour corresponding to the external profile of the crimped section of the sleeve. As the sleeve passes in a heated plastic state continuously between the crimping wheels, the shaped blades crimp the sleeve inwardly from three directions simultaneously, forming a continuous series of closed cells within the sleeve. After passing through the rotating crimping wheels, the periodically crimped sleeve 11 is passed through an arrangement of sprayers 40 which spray cooling water on the sleeve and serve to cool it sutliciently so that it retains its shape. The crimped sleeve then passes around a guide roll 41 and is taken up on a wind-up reel 42 that may be continuously rotated by suitable means (not shown). Thereafter, the crimped sleeve may be covered with the braided outer conductor 21 and the outer insulating sleeve 22 in any conventional manner.

The modied method of making the cable shown in Fig. 7 involves continuously extruding a plastic material 45 from an extruding device 46 containing the usual rotating extruding screw 47 that forces the plastic The radially innermost portion 18 ot' each that are adapted to successively en-v material through an annular die 48 at the delivery end of the extruder, thereby forming the sleeve 11 in a continuous length. 1t will be understood that the extruder 46 is equipped with the usual heating means (not shown) for heating the plastic material 45 to a soft, readily deformable state. A core piece 49 constituting the inner portion of the eXtruder die extends rearwardly of the extruder and has a longitudinal central passageway therethrough, through which the conductor 1t) is fed continuously as the sleeve 11 is extruded. The outer extremity of the core piece 49 is also provided with a gas supply inlet 50 into which moisture free-air, or nitrogen, or other suitable gaseous dielectric may be fed continuously during the extrusion operation. Spaced from the extrusion die in the direction of travel of the sleeve 11 there are arranged a series of crimping wheels S1 which act on the soft, plastic, freshly extruded sleeve 11 in the manner described in connection with Figs. 3 to 6. Thereafter, the crimped sleeve may be cooled and covered with the outer conductor 22 and sleeve in the usual manner.

By either of these methods the improved cable of the present invention can be manufactured rapidly and economically in virtually any suitable desired size.

Because of the manner in which the innermost portions 18 of the crimped areas 14 are pressed into irm contact with the central conductor 1d by the crimping blades, while at the same time the adjacent walls 13, 14 of the crimped sections are pressed together along the radial plane of contact 15, the series of isolated cells 20 thus formed along the length of the cable are tightly sealed off from each other and from the outside atmosphere, so that a liuid dielectric medium introduced therein at the time of manufacture remains within the cable substantially permanently. The dielectric space I'surrounding the central conductor is therefore permanently sealed against the entrance of moisture from the outside, which would impair the dielectric properties of the cable. This construction eliminates any necessity for continuously circulating a dehydrated gas through the cable to provide a perfectly dry atmosphere, as has sometimes been the conventional practice when it was desired to provide optimum electrical properties in the cable.

When the sleeve is crimped inwardly at three equally circumferentially spaced areas in the preferred manner, the desired sealing walls are formed most eiicaciously because 1/3 of the circumference of the sleeve is equal to two times the radius of the sleeve, and therefore when 1/3 of the circumference is deected inwardly it contains just enough material to extend radially inwardly and outwardly along radial lines disposed 120 apart. in this way adjacent crimped portions may be readily urged into firm fluid-tight engagement along adjacent walls without appreciable stretching or crowding of the material.

The crimped construction described provides highly desirable isolated cells without employing excessive amounts of solid dielectric material to form the isolating walls defining the cells. The periodic crimped sections support the central conductor in a stable position at the central axis of the cable, so that the cable is dimensionally stable, and therefore the cable displays little tendency to change its electrical properties as it is handled or ilexed in process of installation. The present construction is also adapted to provide a cable of unusually low capacity since there is very little solid dielectric material in proximity to the central conductor, where its effect on the dielectric loss is the greatest. The outer surface of the insulating sleeve, even though it is crimped inwardly at spaced intervals, still presents an uninterrupted smooth surface over the greater part of the length of the cable, so that there is no difficulty about applying the outer conductor to the surface of the sleeve by the usual braiding operation.

Having thus described my invention, what l claim and desire to protect by Letters Patent is:

In a method of making a coaxial cable the combination of steps comprising forming a length of hollow insulating sleeve from plastic material, disposing a central conductor within the sleeve, charging the sleeve with a huid dielectric medium, crimping the sleeve inwardly in a heated soft state into contact with the conductor at axially spaced points along the length of the sleeve, said crimping being effected at three equally circumferentially spaced areas each constituting one-third of the circumference of the sleeve at each of said points to bring the Walls of circumferentially adjacent crimped areas into contact with each other along radial lines of contact to form sealed cells containing said fluid dielectric, said crimping being eifected substantially Without stretching or crowding of the material of the sleeve, and cooling the sleeve.

References Cited in the rile of this patent UNETED STATES PATENTS 563,273 Guilleaume July 7, 1886 2,029,421 Green et al. Feb. 4, 1936 2,048,450 Horn July 21, 1936 2,123,209 Rost July l2, 1938 2,165,323 White July 11, 1939 2,333,005 Hansell Oct. 26, 1943 FOREGN PATENTS 165,676 Switzerland Nov. 30, 1933 430,581 Great Britain June 2l, 1935 492,397 Great Britain Sept. 20, 1938 692,198 Germany June 14, 1940 867,776 France Nov. 27, 194 

